This statistic shows kernel memory which is allocated, but not in use, and can be broken down by kernel cache (kmem cache). Such a state can occur when memory is freed (for example, when cached file system data is deleted), and the kernel has yet to recover the memory buffers.
An understanding of operating system internals is required to understand this statistic.
When to Check Kernel Memory Allocated, But Not in Use
Rarely. If the dashboard were to show kernel memory as a large consumer of available DRAM (in the Usage: Memory section), then this may be used when troubleshooting the cause. Also see Memory: Kernel Memory in Use.
Kernel Memory Allocated, But Not in Use Breakdowns